1. Field of the Invention
The present invention relates to an active sensor, a multi-point active sensor, a method of diagnosing deterioration of a pipe, and an apparatus for diagnosing deterioration of a pipe, capable of judging existence of a malfunction such as a pipe wall-thickness reduction caused by a high-temperature steam in an atomic power plant and a heat power plant, and a pipe corrosion in a chemical factory and an incineration plant, and capable of identifying the part having a trouble.
2. Description of Related Art
A pipe wall-thickness reduction and a pipe corrosion are conventionally inspected on periodic inspections by using an ultrasonic flaw detecting method and an X-ray transmission method. In the ultrasonic flaw detecting method, a probe that transmits and receives ultrasonic waves is brought into contact with a surface of a pipe, for example, and ultrasonic waves of various frequencies are propagated to an inside (pipe wall part) of the pipe. Then, by receiving the ultrasonic waves that have been reflected on a flaw in the pipe wall part of the pipe or a rear surface of the pipe and returned therefrom, a state of the pipe wall part of the pipe can be grasped.
A position of the flaw can be obtained by measuring a time period between the transmittance of the ultrasonic waves and the reception thereof. A size of the flaw can be obtained by measuring a height of the received echo (intensity of the ultrasonic waves that have been reflected and returned) and a range where the echo appears.
Such an ultrasonic flaw detecting method is mainly used in an atomic power plant, for detecting a plate thickness and a lamination (side cutting appearing in a cut surface of the plate) of a material, and detecting a fusion deficiency of a fused part and a base material by welding, and a crack generated in a thermally affected part. In addition, with respect to a build up welding for reinforcing a nozzle opening, a branch, and a pipe joint, which are disposed around a pressure vessel of an atomic reactor, the ultrasonic flaw detecting method is applied to a base material directly below a build-up welded part, a fused part, and a build-up deposited part (see, Atomic Energy and Design Technique, Okawa Shuppan, (1980), pp. 226 to 250 (Giitiro Uchigasaki, et al.)).
On the other hand, the X-ray transmission method can detect a pipe wall-thickness reduction, without detaching a heat insulation material from the pipe. In the X-ray transmission method, data, which haven been provided by a serial radiographic apparatus such as an X-ray CT scanner, are subjected to a high-speed image processing by using a powerful computer, so as to make an image of the overall object with a fault image showing different X-ray transmittances.
Recently, there is known a method capable of simultaneously taking a picture of substances of different X-ray transmittances, by a simple system including only a sheet-like color scintillator (fluorescent screen) and a CCD camera. The color scintillator emits three primary colors of light, i.e., red (R), green (G), and blue (B), with a luminescent ratio changing in accordance with a transmission amount. This method is used for observing a pipe wall-thickness reduction and for inspecting foreign matters in a thermal/atomic power plant and an oil/chemical complex.
However, in the above ultrasonic flaw detecting method, it is necessary to measure the thickness of a pipe at not less than 1000 positions, and thus it is difficult to conduct the method during a periodic inspection. Further, when the thickness of the pipe is measured, it is necessary to stop the plant in consideration of a temperature constraint, which results in decrease in availability factor.
On the other hand, in the X-ray method capable of detecting a malfunction through the heat insulation member of the pipe, although the method can measure a distribution of the thickness of the pipe, the method is not widely used because an apparatus therefor is expensive.